Is the Electric Force in a Shuttling Ball Experiment Balanced?

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Discussion Overview

The discussion revolves around the "Shuttling Ball Experiment" and whether the electric force acting on a neutral ball, which experiences induced charge, is balanced before it touches the plates. Participants explore the implications of induced charge and the nature of electric forces in a uniform electric field.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that the neutral ball will be attracted to one of the plates due to induced charge, suggesting that the electric force is not balanced.
  • Others reference the textbook, which claims that the electric force on the neutral ball will be balanced by the induced charges, although this is stated without proof.
  • A participant questions the scenario where the ball is not centered between the plates, proposing that the proximity of induced opposite charge to the plate would create an unbalanced force.
  • Another participant counters that in a uniform electric field, the electric force remains constant regardless of the ball's position, implying that forces remain balanced.
  • One participant acknowledges a misunderstanding regarding the nature of forces in a uniform field versus point charges, indicating a shift in their perspective.

Areas of Agreement / Disagreement

Participants express differing views on whether the electric force on the ball is balanced or unbalanced, particularly depending on the ball's position relative to the plates. The discussion remains unresolved, with competing interpretations of the forces at play.

Contextual Notes

Participants note that the textbook's assertion lacks proof, and there is uncertainty regarding the implications of induced charge and the uniformity of the electric field in this context.

Affair
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In my textbook, it states that the ball (neutral) in "Shuttling Ball Experiment" will have induced charge.
Note : The following happens before the ball touches both plates. (There is no conducted charge)

My opinion is : The ball will be attracted to one of the plates. (As there is induced charge)
However, the book states that the electric force (by induced charge) will be balanced. (Stated without proof)

So which one (I or the book) (am / is) wrong ?
If anyone think the book is correct. Can you elaborate the proof here (better with mathematical proof).
 
Last edited:
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Affair said:
In my textbook, it states that the ball (neutral) in "Shuttling Ball Experiment" will have induced charge.
Note : The following happens before the ball touches both plates. (There is no conducted charge)

My opinion is : The ball will be attracted to one of the plates. (As there is induced charge)
However, the book states that the electric force (by induced charge) will be balanced. (Stated without proof)

So which one (I or the book) (am / is) wrong ?
If anyone think the book is correct. Can you elaborate the proof here (better with mathematical proof).

Before the ball touches plate, it is neutral. The induced charges on one side will be balanced by those on the other side. Although there is electric field outside, the electric force acting on the neutral ball is zero.
Note that the ball is stationary initially, you have to apply a force(maybe a slight push) to make it to the plate.
Also note that the ball will decelerate when it is moving towards the plate due to the conservation of energy.
 
Hello Kntsy. Thank you for your reply.

I just wonder what if the ball isn't be placed at the middle (For example : if it is placed close to one plate without touching).
Will it be attracted to the plate due to induced charge ?

In my logic, the induced opposite charge will be closer than the other side of the induced charge. Therefore, the attractive force between the induced opposite charge and the plate will be greater than the repelling force of the induced same charge (on the other side) and the plate.

As a result, isn't that there will be an unbalanced force ?
 
Affair said:
Hello Kntsy. Thank you for your reply.

I just wonder what if the ball isn't be placed at the middle (For example : if it is placed close to one plate without touching).
Will it be attracted to the plate due to induced charge ?

In my logic, the induced opposite charge will be closer than the other side of the induced charge. Therefore, the attractive force between the induced opposite charge and the plate will be greater than the repelling force of the induced same charge (on the other side) and the plate.

As a result, isn't that there will be an unbalanced force ?

Hi,
As the electric field is uniform between the 2 plates, the electric force does not vary with distance from plates. Therefore, the attractive force and the repulsive force is always balanced no matter where you put the ball.
 
Yes, you are right Kntsy.

The key point is "In uniform field, force is independent of distance"

After further checking my logic, I find that I had a wrong concept. I used to think that force is inverse proportional to the square of distance (coulomb's law). I don't realize that only work on point charge (not a uniform field).

Thank you for solving my problem.
 
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